Sign MSIX files with SignTool (workaround solution)
SignTool 64 bit currently cannot sign unsigned .msix files when used with Signing Manager Controller (SMCTL). This limitation stems from the way SignTool handles .msix packages that use certificate-based signing through a Key Storage Provider (KSP).
Nota
To sign MSIX files with 32 bit signtool using office SIPs, see sign with third-party signing tools.
As a workaround, you can use the open-source sign tool provided by Microsoft.
Nota
This tool works only on Windows and with RSA keypairs.